Drone Attacks Q&A: By the Rules

WASHINGTON—The U.S. use of unmanned drones to kill suspected terrorists has prompted a debate over the rules governing the drone program and whether Americans can be targeted.

The New America Foundation, a nonpartisan think-tank in Washington, has counted 420 drone strikes in Pakistan and Yemen since 2004. The foundation's count of people killed isn't as precise: between 1,967 and 3,236. The number of Americans known to have been...